Electric switches often must be operated in low light environments and are therefore frequently back-lit or otherwise illuminated. Many switches also have illuminated graphics, words, or other symbols to identify their functions. For example, switches used to control the lights in an automobile are often illuminated and/or have illuminated symbols to identify their functions.
Symbols on pushbutton switches and similar switches are relatively easy to illuminate because the faces on which the symbols are applied don't move much relative to their back lights when they are operated. However, symbols on thumbwheel switches and other types of switches that rotate are more difficult to illuminate because the surfaces on which the symbols are applied move significantly relative to their back lights when the switches are operated.